Unconjugated idiotypic Ig induces suppression of anti-Id IgG but not IgM antibody and memory B-cell responses. (A-B) Mice were primed with p.Id-FrC fusion DNA vaccine; and 6 weeks later, they either were injected with Id Ig or received no injection. Three days later, the injected animals were divided into 2 groups, and one was boosted with Id-FrC fusion protein (n = 11) and the other group remained unboosted (n = 12). Anti-Id IgG and IgM antibodies were measured one week later by ELISA. (C-D) For ASC, mice were primed and then either received Id Ig (n = 6) or not (n = 6); and 3 days later, both groups were boosted with 100 μg of Id-FrC protein. ASCs were measured 48 hours after the booster injection by ELISPOT. The unboosted control (n = 4) and a separate group, which received a booster injection only, were also included (n = 4). These are combined data of 2 independent experiments. The horizontal bars represent median values. The horizontal line in panel B represents a background level in naive mice (average of 3). **Statistical significance (P < .01). n/s indicates not significant.